US8403445B2 - Method and apparatus for determining the density unevenness in an ink jet head - Google Patents

Method and apparatus for determining the density unevenness in an ink jet head Download PDF

Info

Publication number
US8403445B2
US8403445B2 US12/796,826 US79682610A US8403445B2 US 8403445 B2 US8403445 B2 US 8403445B2 US 79682610 A US79682610 A US 79682610A US 8403445 B2 US8403445 B2 US 8403445B2
Authority
US
United States
Prior art keywords
characteristic values
jet head
ink jet
ink
nozzles
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active, expires
Application number
US12/796,826
Other languages
English (en)
Other versions
US20100315457A1 (en
Inventor
Tadashi Iwasaki
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Riso Kagaku Corp
Original Assignee
Riso Kagaku Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Riso Kagaku Corp filed Critical Riso Kagaku Corp
Assigned to OLYMPUS CORPORATION reassignment OLYMPUS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: IWASAKI, TADASHI
Publication of US20100315457A1 publication Critical patent/US20100315457A1/en
Assigned to ORTEK CORPORATION reassignment ORTEK CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: OLYMPUS CORPORATION
Assigned to RISO KAGAKU CORPORATION reassignment RISO KAGAKU CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: OLYMPUS CORPORATION
Assigned to RISO KAGAKU CORPORATION reassignment RISO KAGAKU CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: ORTEK CORPORATION
Application granted granted Critical
Publication of US8403445B2 publication Critical patent/US8403445B2/en
Active legal-status Critical Current
Adjusted expiration legal-status Critical

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/21—Ink jet for multi-colour printing
    • B41J2/2132—Print quality control characterised by dot disposition, e.g. for reducing white stripes or banding
    • B41J2/2142—Detection of malfunctioning nozzles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/205—Ink jet for printing a discrete number of tones
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/21—Ink jet for multi-colour printing
    • B41J2/2121—Ink jet for multi-colour printing characterised by dot size, e.g. combinations of printed dots of different diameter
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
    • B41J29/38—Drives, motors, controls or automatic cut-off devices for the entire printing mechanism
    • B41J29/393—Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns

Definitions

  • the present invention relates to a method and apparatus for determining the density unevenness that is specific to any ink jet head.
  • Any ink jet printer has an ink jet head that has a plurality of nozzles arranged in a line and configured to eject, for example, ink.
  • a recording medium is transported in a direction perpendicular to the line in which the nozzles of the ink jet head are arranged.
  • the ink head ejects ink to the recording medium so transported, and forms an image on the recording medium.
  • a line head printer i.e., one-pass line head printer
  • a recording medium is transported below the ink jet head one time, thereby to form an image on the recording medium.
  • the nozzles eject ink in different volumes (or amounts). That is, the amount of ink ejected from each nozzle differs that of ink ejected from any other nozzle.
  • the difference in the amount of ink injected lowers the quality of the image formed on the recording medium in most cases.
  • the one-pas line heat printer may have inconvenience that results from, for example, the degrading of image quality. It is therefore useful to determine the difference between the nozzles in terms of the amount of ink ejected, in order to distinguish a good ink jet head from a defective one.
  • the method disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-092966 can be utilized.
  • the publication discloses a method of detecting streaks on a sheet-shaped object.
  • the publication discloses an algorithm of comparing a plurality of line data items, one with another, and regarding any data item that changes more than a predetermined value, as a data time that represents an uneven streak.
  • a method of determining the density unevenness of an ink jet head comprises calculating characteristic values about ink amounts ejected from all nozzles of the ink jet head, respectively; arranging the characteristic values in the order the nozzles are arranged and calculating a decision parameter from changes in the characteristic values about those of the nozzles, which exit in a predetermined section; and comparing the decision parameter with a predetermined threshold value, thereby determining the density unevenness of the ink jet head.
  • An apparatus for determining the density unevenness of an ink jet head comprises a characteristic data generation unit configured to calculate characteristic values about ink amounts ejected from all nozzles of the ink jet head, respectively; a decision parameter acquisition unit configured to arrange the characteristic values in the order the nozzles are arranged and to calculate a decision parameter from changes in the characteristic values about those of the nozzles, which exit in a predetermined section; and a decision unit configured to compare the decision parameter with a predetermined threshold value, thereby determining the density unevenness of the ink jet head.
  • FIG. 1 is a block diagram showing an apparatus according to a first embodiment of this invention, which is designed to determine density unevenness of an ink jet head;
  • FIG. 2 is a diagram showing the nozzles arranged in a line in the ink jet head inspected by the apparatus
  • FIG. 3 is a flowchart explaining how the apparatus determines the density unevenness
  • FIG. 4 is a schematic diagram explaining how the ink jet head performs test printing
  • FIG. 5 is a diagram showing exemplary characteristic values related to ink amount, which has been generated by the characteristic data generation unit provided in the apparatus;
  • FIG. 6 is a diagram showing the first and second envelopes acquired by the envelope acquisition unit provided in the apparatus.
  • FIG. 7 is a diagram explaining how the parameter acquisition unit provided in the apparatus acquires decision parameters
  • FIG. 8 is a flowchart explaining how the decision parameters are calculated in the embodiment.
  • FIG. 9 is a flowchart explaining how the apparatus determines the density unevenness
  • FIG. 10 is a diagram illustrating the relation between the rank of density unevenness and the threshold value
  • FIG. 11 is a flowchart explaining how the decision parameters are calculated in a first modification of the apparatus according to this invention, which is designed to determine the density unevenness of an ink jet head;
  • FIG. 12 is a flowchart explaining how the first modification determines the density unevenness
  • FIG. 13 is a diagram illustrating the relation the ranks of density unevenness have with the threshold values in the first modification
  • FIG. 14 is a diagram showing a characteristic value indicating a wave of cycle in terms of dot diameter, the value having been acquired by the envelope acquisition unit provided in a second modification of the apparatus according to this invention
  • FIG. 15 is a diagram prepared by extracting the waveforms of characteristic values, each lasting for cycle ⁇ , and then by superimposing these waveforms one on another, and showing how the dot diameter changes within one cycle ⁇ ;
  • FIG. 16 is a diagram explaining how a characteristic value of the density unevenness of an ink jet printer is generated in an apparatus according to a second embodiment of this invention, which is designed to determine density unevenness;
  • FIG. 17 is a perspective view of an ink jet head which has two nozzle columns for forming two lines in the same recording area of a recording medium, and whose density unevenness is to be determined by an apparatus according to a third embodiment of this invention;
  • FIG. 18 is a diagram showing a distribution of the diameters of test dots formed by two nozzle columns of the apparatus according to third embodiment.
  • FIG. 19 is a diagram showing a distribution of dot diameters in the apparatus according to the third embodiment, prepared by subtracting the dot-diameter distribution for one nozzle column from the dot-diameter distribution for the other nozzle column.
  • FIG. 1 is a block diagram showing an apparatus 1 according to the first embodiment of the invention, which is designed to determine density unevenness of an ink jet head.
  • the apparatus 1 has a main control unit 2 constituted by, for example, a CPU.
  • a program memory 4 a data memory 5 , a console unit 6 , a display 7 and an external input unit 8 are connected by a bus 3 .
  • the console unit 6 is composed of, for example, a keyboard and a mouse.
  • the display 7 is, for example, a liquid crystal display.
  • the external input unit 8 inputs various data items through a communication line etc.
  • the various data items are, for example, characteristic values about the amounts of ink ejected from the nozzles 21 - 1 to 21 - n provided in, for example, such an ink jet head 20 as shown in FIG. 2 .
  • the data memory 5 temporarily stores the data that has been processed in accordance with the instructions issued from the main control unit 2 .
  • the program memory 4 stores a density-unevenness determination program for determining the density unevenness that is specific to the ink jet head 20 .
  • the density-unevenness determination program is used to generate characteristic values about the ink amounts to eject from all nozzles 21 - 1 to 21 - n of the ink jet head 20 , to arrange all characteristic values in the order the nozzles 21 - 1 to 21 - n are arranged, to calculate decision parameters from the differences between some of the characteristic values so arranged, and to compare the decision parameters, thus calculated, with a predetermined threshold value.
  • the density unevenness specific to the ink jet head 20 is thereby determined.
  • the main unit 2 executes the density-unevenness determination program stored in the program memory 4 , controlling a characteristic data generation unit 9 , a filtering process unit 10 a , a parameter calculation unit 10 c and a decision unit 11 .
  • the characteristic data generation unit 9 calculates characteristic values about the ink amounts to eject from all nozzles 21 - 1 to 21 - n of the ink jet head 20 . More specifically, the characteristic data generation unit 9 generates one data item selected from the group consisting of the ink amount ejected from each nozzle, the diameter of the ink drop ejected from the nozzle, the diameter of ink dot formed as the ink ejected lands a recording medium, the area of the ink dot, the optical density of the ink dot, the diameter of the nozzle, the resistance or electrostatic capacitance of the actuator that ejects the ink through the nozzle and the size of the nozzle.
  • the apparatus 1 has a decision parameter acquisition unit 10 .
  • the decision parameter acquisition unit 10 prepares such a characteristic graph as shown in FIG. 6 , by arranging the characteristic values calculated for the nozzles 21 - 1 to 21 - n by the characteristic data generation unit 9 , in accordance with the order the nozzles 21 - 1 to 21 - n are arranged.
  • the characteristic graph thus prepared, shows how the dot diameter changes in accordance with the position of the nozzle.
  • the nozzles of the ink jet head 20 are assigned to nozzle numbers “ 21 - 1 ” to “ 21 - n ,” respectively, in accordance with the order they are arranged. As seen from in FIG.
  • the decision parameter acquisition unit 10 first scans a section S preset in the characteristic graph (hereinafter called “decision section S,” in the direction in which the nozzles 21 - 1 to 21 - n are arranged, and then acquires a decision parameter on the basis of the largest change in each characteristic value existing in the decision section S.
  • the decision section S extends in the direction the nozzles 21 - 1 to 21 - n are arranged, and has a width that corresponds to only some of all characteristic values. For example, the decision section S has a width corresponding to nozzle numbers “k” to “k+s ⁇ 1.”
  • FIG. 7 shows how the dot diameter changes in only the second envelope Eb for the minimum dot diameter, not showing the first envelope Ea.
  • the decision parameter acquisition unit 10 has a filtering process unit 10 a , an envelope acquisition unit 10 b , and a parameter calculation unit 10 c.
  • the filtering process unit 10 a performs a filtering process on the characteristic values the characteristic data generation unit 9 has acquired about all ink amounts, for example the characteristic values about the density unevenness resulting from asymmetry, thereby accomplishing smoothing.
  • the envelope acquisition unit 10 b acquires envelopes that accord with the changes that the respective characteristic values processed by the filtering process unit 10 a have undergone. To be more specific, the envelope acquisition unit 10 b acquires such two envelopes Ea and Eb as shown in FIG. 6 . These envelopes Ea and Eb accord with the largest and smallest changes, respectively, in the various characteristic values such as dot diameter.
  • the parameter calculation unit 10 c scans the decision section S in the direction the nozzles 21 - 1 to 21 - n are arranged, with respect to one of the envelopes Ea and Eb acquired by the envelope acquisition unit 10 b as shown in FIG. 7 . As it scans the envelope Ea or Eb, the parameter calculation unit 10 c detects the largest change in the characteristic value. Then, the parameter calculation unit 10 c calculates a decision parameter from the largest change in the characteristic value.
  • the decision unit 11 compares the decision parameter calculated by the parameter calculation unit 10 c , with the predetermined threshold value, thus determining the degree of the density unevenness specific to the ink jet head 20 .
  • the apparatus 1 determines the density unevenness in four steps M 1 to M 4 .
  • Step M 1 the characteristic value about the density unevenness of the ink jet head 20 is generated, in order to determine whether the apparatus 1 is a good ink jet head or a defective one.
  • Step M 2 the characteristic value is subjected to the filtering process.
  • Step M 3 a decision parameter is calculated from the characteristic value subjected to the filtering process.
  • Step M 4 the degree of the density unevenness specific to the ink jet head 20 is determined from the decision parameter.
  • the characteristic data generation unit 9 generates characteristic values about the ink amounts ejected from all nozzles 21 - 1 to 21 - n of the ink jet head 20 .
  • the characteristic value pertaining to each of the nozzles 21 - 1 to 21 - n is one data item selected from the group consisting of the ink amount (mass or amount) ejected from the nozzle, the diameter of the ink drop ejected from the nozzle, the diameter of ink dot formed as the ink ejected lands a recording medium, the area of the ink dot, the optical density of the ink dot, the diameter of the nozzle, the resistance or electrostatic capacitance of the actuator that ejects the ink through the nozzle and the size of the nozzle.
  • FIG. 4 is a schematic diagram explaining how the ink jet head 20 performs test printing.
  • the ink jet head 20 has, in the bottom, a plurality of nozzles 21 - 1 to 21 - n , for example in number NZL.
  • the ink jet head 20 is an ink jet head of on-demand type.
  • the ink jet head 20 has actuators of, for example, piezoelectric type or thermal type.
  • the ink jet head 20 further has channels connected to the nozzles 21 - 1 to 21 - n , respectively. Each channel contains ink.
  • the actuators are provided on the walls of the channels connected to the respective nozzles 21 - 1 to 21 - n .
  • a recording medium 31 is placed, opposing to the ink jet head 20 .
  • each actuator contracts and expands in response to an external signal 30 supplied from an external apparatus.
  • the actuators are provided on the channels of the nozzles 21 - 1 to 21 - n , respectively, which are configured to eject ink.
  • the pressure changes in the channel on which the actuator is provided.
  • the ink contained in the channel is ejected from the nozzle (nozzle 21 - 1 , 21 - 2 , . . . or 21 - n ).
  • the ink ejected from each nozzle forms a test dot 32 on the recording medium 31 .
  • the density unevenness specific to the ink jet head 20 largely results from the difference between the nozzles 21 - 1 to 21 - n in terms of the amount of ink ejected, or the difference between the nozzles 21 - 1 to 21 - n in terms of the angle at which ink is ejected.
  • the difference in amount of ink ejected is evaluated.
  • the characteristic value for evaluating the difference in amount of ink ejected is related to the amounts of ink the nozzles 21 - 1 to 21 - n of the ink jet head 20 eject.
  • the characteristic value related to the amount of ink ejected by a nozzle is, for example, the diameter of a circle 33 circumscribing the test dot 32 formed by the ink ejected from the nozzle and not contacting the test dot formed by the ink ejected from any other nozzle in the same condition.
  • the diameter of the circle 33 circumscribing the test dot 32 will be referred to as “dot diameter.”
  • Dot diameter (n) means the diameter of the dot formed by the nth nozzle.
  • the recording medium 31 should best be a glossy paper sheet for use in ink jet printers.
  • the characteristic value may be other than the amount of ink ejected, for example either the amount of the ink drop ejected, measured by an optical means, or the area of the test dot 32 formed on the recording medium 31 .
  • the characteristic value may be the density or brightness of a painted-out image formed on the recording medium 31 .
  • a transport means is provided to transport the ink jet head 20 or the recording medium 31 .
  • the ink jet head 20 may be held immovable, and the transport means transports the recording medium 31 below the ink jet head 20 .
  • the ink jet head 20 emits ink dots onto the recording medium 31 , forming a solid image thereon. Either an optical densitometer or a chromoscope measures the density or brightness of the solid image which is used as characteristic value.
  • the characteristic value can achieve some effect if it is the diameter of the nozzle (nozzle 21 - 1 , 21 - 2 , . . . or 21 - n ), the resistance or electrostatic capacitance of the actuator or the size of the channel containing ink, or the like, which greatly influences the amount of ink ejected.
  • the density unevenness can be determined from one of these characteristic values, without actually ejecting the ink from the nozzle. Therefore, any one of these characteristic values may be selected in accordance with the degree of density unevenness and can be used to determine the density unevenness.
  • the characteristic value need not be a single physical quantity. Rather, it may be a weighted average of two or more physical quantities. For example, it may be 4 ⁇ dot area/dot circumference, i.e., known as hydraulic diameter in the field of hydraulics. This characteristic value is preferable because it is hardly influenced by, for example, the running of ink on the recording medium 31 .
  • Step M 2 the ink jet head 20 performs the filtering process on the characteristic values about all ink amounts, acquired by the characteristic data generation unit 9 , thereby accomplishing smoothing.
  • the filtering process uses a well-known digital filter such as a motion-average, finite impulse response (FIR) filter or an infinite impulse response (IIR) filter.
  • FIR finite impulse response
  • IIR infinite impulse response
  • the filtering process it is desirable to utilize a low-pass filter that filters out components other than those of special frequency, which are conspicuous to the human eye.
  • the components filtered out are, for example, those that have wavelengths less than or equal to 1 mm.
  • the filtering process may use a high-pass filter that filters out low-frequency components having wavelengths greater than or equal to, for example, 200 mm.
  • the filtering process may use a band pass filter that is a combination of a low-pass filter and a high-pass filter. The filtering process need not be performed, depending on the method that is employed to acquire the characteristic values.
  • the filtering process according to the present embodiment uses a low-pass filter that filters out components having wavelengths less than or equal to 1 mm, with respect to the dot diameter that has been selected as characteristic value.
  • the envelope acquisition unit 10 b arranges the dot diameters generated by the characteristic data generation unit 9 in the order the nozzles 21 - 1 to 21 - n are arranged, as is illustrated in FIG. 6 , thus preparing a characteristic graph that shows the relation between the dot diameters, on the one hand, and the positions of the nozzles 21 - 1 to 21 - n . From the characteristic graph, the envelope acquisition unit 10 b acquires two envelopes Ea and Eb that accord with the largest and smallest changes, respectively, the dot diameters undergo at the positions of the nozzles 21 - 1 to 21 - n . More specifically, as shown in FIG.
  • the envelope Ea (hereinafter called “first envelope”) is defined by a third-degree spline curve or the like, and pertains to the maximum value
  • the envelope Eb (hereinafter called “second envelope”) is defined by a third-degree spline curve or the like, and pertains to the minimum value.
  • Step M 3 the parameter calculation unit 10 c sets a decision section S for the first envelope Ea or the second envelope Eb acquired in Step M 3 and pertaining to the maximum value and minimum value, respectively.
  • the parameter calculation unit 10 c then scans the decision section S in the direction the nozzles 21 - 1 to 21 - n are arranged in a specific order, calculating a decision parameter from the change the first envelope Ea or second envelope Eb undergoes in the decision section S.
  • the decision parameter is a parameter used to determine the density unevenness of the ink jet head 20 .
  • the decision parameter is the largest change observed in the decision section S, of the first envelope Ea or second envelope Eb acquired by the envelope acquisition unit 10 b.
  • the parameter calculation unit 10 c sets the decision section S as shown in FIG. 7 .
  • the decision section S is preferably “100,” on the assumption that the ink jet head 20 has resolution of, for example, 300 dpi.
  • the decision section S is a natural number not exceeding NZL, i.e., the number of nozzles 21 - 1 to 21 - n the ink jet head 20 has.
  • the decision section S is set in order to detect regions in which the first and second envelopes Ea and Eb greatly change. The regions detected are, for example, those in which the test dot 32 formed on the recording medium 31 changes greatly in diameter. If the decision section S is expanded in width, regions where the test dot 32 changes greatly in diameter can be detected in a broader range. Conversely, if the is contracted, the regions where the test dot 32 changes greatly in diameter can be detected in a narrower range.
  • the elements of Ti are equal, in numbers, to NZL-s+1, where NZL is the number of all nozzles and i is an envelope index.
  • two envelopes, i.e., Ea and Eb exist in the present embodiment, and two work arrays T 1 and T 2 therefore exist.
  • FIG. 7 shows the second envelope Eb only, and therefore shows the work array T 2 pertaining to the second envelope Eb.
  • Step M 3 - 5 the parameter calculation unit 10 c substitutes the maximum value for Ti(k) for the decision parameter. In Step M 3 - 5 , the parameter calculation unit 10 c then increases k to k+1, moving the decision section S.
  • the work array T 1 is T 2 for the second envelope Eb shown in FIG. 7 .
  • the parameter calculation unit 10 c therefore scans the decision section S, in the range from the nozzle number “k” to the nozzle number “ 21 - n .” As the parameter calculation unit 10 c so scans the decision section S, it calculates the maximum value max and minimum value min of that part of the second envelope Eb, which lies in the decision section S. The parameter calculation unit 10 c then finds the difference T 2 ( k ) between the maximum value max and minimum value min, which are in the range of the nozzle numbers “k” to “ 21 - n .” Further, the parameter calculation unit 10 c calculates a decision parameter from the difference T 2 ( k ) between the maximum value max and minimum value min. In this embodiment, the decision parameter is equivalent to the average change rate of the characteristic value, for the decision section S.
  • Step M 4 the decision unit 11 compares the decision parameter calculated by the parameter calculation unit 10 c with the predetermined threshold value, determining the density unevenness of the ink jet head 20 .
  • rank “1,” rank “2” and rank “3,” are set to the density unevenness, and the density unevenness is evaluated at rank “1,” rank “2” or rank “3.”
  • Step M 4 - 1 the decision unit 11 sets threshold values Th 1 and Th 2 .
  • Threshold values Th 1 and Th 2 are determined from the relation between the decision parameters acquired of a plurality of ink jet heads 20 and, for example, the function evaluation of the solid image printed on a recording medium. Generally, the relation of Th 1 ⁇ Th 2 is established.
  • threshold value Th 1 and any threshold value smaller than Th 1 are evaluated at rank “1.” Any threshold value between threshold values Th 1 and Th 2 is evaluated at rank “2.” Threshold value Th 2 and any threshold value larger than Th 2 are evaluated at rank “3.” Therefore, any ink jet head will be evaluated as a good one even if the decision parameter is less than or equal to threshold value Th 1 , because the rank of its density unevenness is lower than rank “2” and rank “3.”
  • Step M 4 - 2 the decision unit 11 determines whether the decision parameter is smaller than threshold value Th 1 (decision parameter ⁇ threshold value Th 1 ).
  • Step M 4 - 3 determines that the ink jet head 20 is evaluated at rank “1.”
  • Step M 4 - 4 the decision unit 11 determines whether the decision parameter is greater than or equal to threshold value Th 2 (decision parameter threshold value Th 2 ).
  • the decision unit 11 determines that the ink jet head 20 is evaluated at rank “2.” That is, the decision parameter is somewhere between threshold values Th 1 and Th 2 .
  • Step M 4 - 6 the decision unit 11 determines that the ink jet head 20 is evaluated at rank “3.” The decision parameter is therefore greater than or equal to threshold value Th 2 .
  • the characteristic values about ink amounts to be ejected from the nozzles 21 - 1 to 21 - n of the ink jet head 20 are acquired for all nozzles 21 - 1 to 21 - n in the first embodiment described above. Then, the characteristic values arranged in the order the nozzles 21 - 1 to 21 - n are arranged.
  • decision parameters are calculated from the changes the first envelope Ea and second envelope Eb, i.e., arrays of the characteristic values, undergo in the decision section S.
  • the decision parameters are compared with threshold values Th 1 and Th 2 .
  • the density unevenness specific to the ink jet head 20 is determined.
  • the specific density unevenness can evaluated at, for example, rank “1,” rank “2” or rank “3,” in accordance with the degree of the density unevenness specific to the ink jet head 20 .
  • This embodiment can appropriately determine or evaluate the density unevenness of the ink jet head 20 , from the large spatial changes in the characteristic values such as dot diameters, as is shown in the flowchart of determining the density unevenness.
  • the density unevenness is determined as shown in FIG. 3 . That is, the characteristic value of the ink jet head 20 is generated in Step M 1 , the characteristic value is subjected to the filtering process in Step M 2 , a decision parameter is calculated in Step M 3 from the characteristic value subjected to the filtering process, and the density unevenness of the ink jet head 20 is determined from the decision parameter. Nonetheless, Steps M 1 to M 3 need not be so distinctly performed.
  • the characteristic value calculated may be used as a filtering process decision parameter, as well, as in the third embodiment that will be described later.
  • the first embodiment described above calculates the decision parameter from two types of envelopes, i.e., first envelope Ea and second envelope Eb.
  • the invention is not limited to this.
  • the decision parameter may be calculated by using, for example, the characteristic value that has been subjected to the filtering process.
  • the first embodiment evaluates the density unevenness at one of three ranks.
  • the number of ranks is not limited “3,” nevertheless.
  • the ranks may be set in a different number.
  • the density unevenness may not be ranked at all.
  • the decision parameter may be used as the result of determining the density unevenness.
  • the density unevenness may be determined directly from the decision parameter, which is used as a score representing the degree of the decision parameter.
  • the first embodiment calculates the decision parameter from only those parts of the first envelope Ea and second envelope Eb, which change more greatly than any other parts.
  • This invention is not limited to this.
  • the changing parts of the first envelope Ea and second envelope Eb may be ranked in terms of change magnitude, some of the changing parts, which are ranked over a preset range, may be weighted, and the average weight of these parts may be used as decision parameter.
  • a plurality of decision sections S having different widths are set, and threshold values are set to the decision sections S, respectively.
  • Step M 3 shown in FIG. 3 the change each characteristic value undergoes in the decision section S on the array of characteristic values is determined.
  • Step M 4 the change thus determined is compared with a threshold value.
  • Step M 3 one decision parameter is calculated for the density unevenness. Nonetheless, a plurality of decision parameters should better be calculated in Step S 3 . If the decision sections S have different widths, the different threshold values Th 1 are applied to the decision sections S, respectively, in most cases.
  • the decision parameter for the decision section S ⁇ 100
  • the average change rate of dot diameter i.e., the average change rate of dot diameter
  • Step M 3 How to calculate the decision parameter for determining the density unevenness (Step M 3 ) in the case where n decision parameters exists will be explained first with reference to the flowchart of FIG. 11 .
  • Step M 4 how to determine the density unevenness of the ink jet head 20 (Step M 4 ) will be explained with reference to the flowchart of FIG. 12 .
  • Step M 3 - 10 the parameter calculation unit 10 c sets m decision sections S.
  • Index J is initialized to “0.”
  • Step M 3 - 11 the parameter calculation unit 10 c initializes index k to “0,” and initializes the work array Ti pertaining to the ith envelope to ⁇ 0, . . . , 0 ⁇ .
  • the work array Ti has as many elements as NZL-s(j)+1.
  • Step M 3 - 12 the parameter calculation unit 10 c substitutes, for the work array Ti(k), the difference between the maximum and minimum values of the ith envelope for the nozzles having nozzle numbers k to k+s ⁇ 1.
  • Step M 3 - 14 the parameter calculation unit 10 c substitutes, for the decision parameter (j), the maximum and minimum values for i and k of the work array Ti(k). Then, in Step M 3 - 15 , the parameter calculation unit 10 c increases k to k+1, moving the decision section S. Thereafter, the parameter calculation unit 10 c returns to Step M 3 - 12 .
  • the decision unit 11 determines the degree of density unevenness of the ink jet head 20 on the basis of the decision parameter calculated by the parameter calculation unit 10 c .
  • the density unevenness is ranked at one of three ranks in the first modification, as in the first embodiment.
  • the ink jet head 20 is evaluated as best if its density unevenness is set to rank “1,” as second best if its density unevenness is set to rank “2,” and as worst if its density unevenness is set to rank “1.”
  • FIG. 13 illustrates the relation the ranks “1” to “3” of density unevenness have with the decision sections S and threshold values Th 1 and Th 2 for decision parameters.
  • the decision sections S have been set to different ranges (e.g., 5, 10, 30, 60 and 100).
  • the threshold values Th i.e., Th 1 and Th 2 ) have different values and are set for each decision section S.
  • Step M 4 - 11 the decision unit 11 determines whether the decision parameters (k) ( ⁇ Th 1 ( k )) are available for all k. If the decision parameters (k) ( ⁇ Th 1 ( k )) are available for all k, or if Yes, the decision unit 11 goes to Step M 4 - 12 . In Step M 4 - 12 , the decision unit 11 determines that the jet ink head 20 is evaluated at rank “1,” and then terminates the decision sequence.
  • Step M 4 - 13 determines whether any decision parameter (k) that is greater than or equal to Th 2 ( k ) (k ⁇ Th 2 ( k )). If a decision parameter (k) greater than or equal to Th 2 ( k ) exists, or if Yes, the decision unit 11 goes to Step M 4 - 14 and determines that the ink jet head 20 is evaluated at rank “3,” and terminates the decision sequence.
  • Step M 4 - 15 determines that the ink jet head 20 is evaluated at rank “2,” and terminates the decision sequence.
  • the first modification In the first modification of the first embodiment, decision sections S of different widths are set, threshold values Th are set for these decision sections S, respectively, decision parameters are calculated for the respective decision sections S from the changes in the characteristic values manifested on the array of decision parameters, and the decision parameters for the respective decision sections S are compared with the threshold values. The density unevenness of the ink jet head 20 is thereby determined.
  • the first modification achieves the same advantages as the first embodiment described above.
  • decision parameters are calculated in Step M 3 from the changes less than the characteristic values and observed in the associated decision section S, if the envelope cyclically changes on the array of all characteristic values.
  • FIG. 14 shows an envelope, or a wave, observed on the array of all characteristic values that accord with the order in which the nozzles 21 - 1 to 21 - n of the ink jet head 20 are arranged, e.g., dot diameters (i.e., diameters of the circles 33 circumscribing the test dots 32 ).
  • dot diameters i.e., diameters of the circles 33 circumscribing the test dots 32 .
  • the dot diameter changes like waves of cycle ⁇ , generally decreasing toward the right little by little. This changing of the dot diameter is too little to be conspicuous to the human eye.
  • FIG. 15 has been prepared by extracting the waveforms of the characteristic values shown in FIG. 14 , each lasting for cycle ⁇ , and then by superimposing these waveforms one on another. That is, FIG. 14 shows an envelope observed on the array of dot diameters that accord with the order in which the nozzles 21 - 1 to 21 - n of the ink jet head 20 are arranged in the order of their numbers. By contrast, FIG. 15 shows how the dot diameter changes within one cycle ⁇ .
  • cycle ⁇ may be used as a variable.
  • Cycle ⁇ may be defined as pertaining to that part of the envelope, which undergoes the largest undulation.
  • the decision parameter may be, for example, the highest-order coefficient of an approximate curve representing the characteristic value.
  • the second modification calculates the decision parameter, in Step M 3 , from the changes less than the characteristic values and observed on the envelope in the decision section S corresponding to the cycle, if the envelope observed on the array of all characteristic values changes cyclically.
  • the second modification can, therefore, determine the cyclic density unevenness more accurately than otherwise.
  • Step M 1 not only the characteristic values acquired for the respective nozzles 21 - 1 to 21 - n , but also the angles at which the nozzles 21 - 1 to 21 - n eject ink or the deviations of the ink-landing positions on the recording medium 31 are cumulated in Step M 1 , thereby calculating characteristic values for the density unevenness of the ink jet head 20 .
  • the first embodiment described above determines the degree of density unevenness from only the characteristic values reflecting the amounts of ink the nozzles 21 - 1 to 21 - n of the ink jet head 20 eject.
  • this embodiment determines the degree of density unevenness from not only the characteristic values reflecting the amounts of ink, but also the angles at which the nozzles 21 - 1 to 21 - n eject ink or the deviations of the ink-landing positions on the recording medium 31 .
  • the kth test dot 32 should best be at distance x from an adjacent test dot, i.e., (k ⁇ 1)th test dot 32 , and also at distance x from the other adjacent test dot, i.e., (k+1)th test dot 32 .
  • the kth test dot 32 may be closer to the (k ⁇ 1)th test dot 32 , deviated by distance d from the ideal position D.
  • ⁇ xd/x and ⁇ xd/x are added to, for example, the ⁇ 1th characteristic value and the (k+1)th characteristic value, respectively, in the second embodiment. This process serves to evaluate such density unevenness that the density is high where test dots 32 are little spaced from one another and is low where test dots 32 are much spaced from one another.
  • the rate of sampling characteristic values may be locally changed. That is, the characteristic values once sampled as (nozzle number, characteristic value (nozzle number)) may be re-sampled in the form of (1, characteristic value (1), (2, characteristic value (2)), . . . , (k ⁇ 1, characteristic value (k ⁇ 1)), (k ⁇ d/x, characteristic value (k)), (k+1, characteristic value (k+1)), . . . , (n, characteristic value (n)).
  • the second embodiment determines the density unevenness of the ink jet head 20 , on the basis of not only the amounts of ink ejected, but also the difference between the nozzles in terms of ink ejection angle.
  • the second embodiment can therefore determine the degree of density unevenness more accurately than otherwise.
  • the ink jet head 20 may be of the type that has a plurality of nozzle columns, each column composed of nozzles 21 - 1 to 21 - n , and may be designed to apply ink drops emitted from the nozzles of any column land on the recording medium 31 , at the same positions as the ink drops emitted from the nozzles of any other column, thus forming a line-like recording area.
  • the amount of ink emitted from all nozzles of each nozzle column is calculated as a characteristic value in Step M 1 of generating the characteristic data representing the density unevenness of the ink jet head 20 , and the difference between the characteristic values for the nozzle columns is acquired as a characteristic value.
  • the ink jet head 20 has nozzle columns, each composed of nozzles 21 - 1 to 21 - n arranged in a column as illustrated in FIG. 17 . More precisely, the ink jet head 20 has two nozzle columns 34 and 35 . The ink drops ejected from the nozzles of the nozzle column 34 and the ink drops ejected from the nozzles of the nozzle column 35 land in the same recording area of the recording medium 31 . The ink jet head 20 of this type is used to form a high-quality image on the recording medium 31 .
  • the nozzle columns 34 and 35 each having nozzles 21 - 1 to 21 - n , may be driven by one drive unit made of piezoelectric sintered material. In this case, the nozzle columns 34 and 35 eject ink in the same amount in most cases. If this characteristic of the ink jet head is utilized, the characteristic value of density unevenness can be efficiently filtered in Step M 2 .
  • the nozzle columns 34 and 35 of the ink jet head 20 shown in FIG. 17 are so arranged that the nozzles 21 - 1 to 21 - n of one column are displaced by half the nozzle interval from the nozzles 21 - 1 to 21 - n of the other column, respectively. Therefore, the ink jet head 20 has resolution twice that of an ink jet head that has one column of nozzles.
  • the actuators provided for each nozzle column have been made by cutting one piezoelectric element.
  • the nozzle columns 34 and 35 of the ink jet head 20 may be asymmetric to each other, because of the specific structure of the ink jet head 20 or because of the method of forming the nozzle columns 35 and 36 .
  • the ink jet head 20 form such test dots 32 as shown in FIG. 5 .
  • the diameter distribution of test dots 32 is a combination of the diameter distribution of test dots formed by the nozzle column 34 and the diameter distribution of test dots formed by the nozzle column 35 . As shown in FIG.
  • the diameter distribution of the dots formed by the nozzle column 34 differs from that of the dots formed by the nozzle column 35 , because of the asymmetry resulting from the structure of the ink jet head 20 or from the method of forming the nozzle columns 35 and 36 .
  • the short-cycle fluctuation of the diameter distribution of dots formed by the nozzle column 35 is superimposed on the diameter distribution of dots formed by the nozzle column 34 , as shown in FIG. 18 .
  • the fluctuation therefore reflects the cycle of diameter distribution of dots formed by the nozzle column 35 . If the diameter distribution of dots formed by the nozzle column 34 is subtracted from that of dots formed by the nozzle column 35 , only the short-cycle fluctuation due to the nozzle column 35 will then appear as shown in FIG. 19 .
  • the short-cycle fluctuation due to the nozzle column 35 represents the density unevenness that has resulted from the structure of the ink jet head or the method of forming the nozzle columns.
  • the filtering process unit 10 a subtracts the diameter distribution of dots formed by the nozzle column 34 is subtracted from that of dots formed by the nozzle column 35 , thereby finding the short-cycle fluctuation due to the nozzle column 35 .
  • the density unevenness due to the asymmetry resulting from the structure of the ink jet head or the method of forming the nozzle columns may be negligibly small. In this case, it is sufficient to evaluate the density unevenness resulting from only the nozzle column 34 or 35 , as in the first embodiment. This is desirable, because half the amount of data involves in calculating the density unevenness.

Landscapes

  • Engineering & Computer Science (AREA)
  • Quality & Reliability (AREA)
  • Ink Jet (AREA)
  • Accessory Devices And Overall Control Thereof (AREA)
US12/796,826 2009-06-11 2010-06-09 Method and apparatus for determining the density unevenness in an ink jet head Active 2031-06-15 US8403445B2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2009-140168 2009-06-11
JP2009140168A JP5322786B2 (ja) 2009-06-11 2009-06-11 インクジェットヘッドの濃度ムラ判定方法及びその装置

Publications (2)

Publication Number Publication Date
US20100315457A1 US20100315457A1 (en) 2010-12-16
US8403445B2 true US8403445B2 (en) 2013-03-26

Family

ID=43306078

Family Applications (1)

Application Number Title Priority Date Filing Date
US12/796,826 Active 2031-06-15 US8403445B2 (en) 2009-06-11 2010-06-09 Method and apparatus for determining the density unevenness in an ink jet head

Country Status (2)

Country Link
US (1) US8403445B2 (ja)
JP (1) JP5322786B2 (ja)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20150062224A1 (en) * 2013-08-27 2015-03-05 Fujifilm Corporation Ink jet recording apparatus and method
CN110877484A (zh) * 2018-09-06 2020-03-13 系统科技公司 喷墨印刷方法及喷墨印刷设备
US10632759B2 (en) * 2017-12-18 2020-04-28 Seiko Epson Corporation Printing control apparatus, printing control system, and printing control method

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103080941A (zh) 2010-08-24 2013-05-01 旭硝子株式会社 计算用数据生成装置、计算用数据生成方法及计算用数据生成程序
KR102170962B1 (ko) * 2018-12-10 2020-10-28 (주)에스티아이 잉크젯 인쇄 방법 및 잉크젯 인쇄 장치

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001092966A (ja) 1999-09-21 2001-04-06 Konica Corp 画像処理方法及び画像処理装置
US20030086100A1 (en) * 2001-11-06 2003-05-08 Canon Kabushiki Kaisha Image correction method in inkjet recording apparatus
US20050260004A1 (en) * 2004-05-07 2005-11-24 Canon Kabushiki Kaisha Color image forming apparatus and control method therefor

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH05301426A (ja) * 1992-04-27 1993-11-16 Canon Inc 記録装置
JP2001310498A (ja) * 2000-04-28 2001-11-06 Canon Inc 画像記録装置および画像記録方法
JP4227395B2 (ja) * 2002-11-14 2009-02-18 キヤノン株式会社 液滴吐出状態判定方法及び装置とインクジェットプリンタ及びそのプログラムと記憶媒体
JP2006168139A (ja) * 2004-12-15 2006-06-29 Canon Inc インクジェット記録装置及びインクジェット記録方法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001092966A (ja) 1999-09-21 2001-04-06 Konica Corp 画像処理方法及び画像処理装置
US20030086100A1 (en) * 2001-11-06 2003-05-08 Canon Kabushiki Kaisha Image correction method in inkjet recording apparatus
US20050260004A1 (en) * 2004-05-07 2005-11-24 Canon Kabushiki Kaisha Color image forming apparatus and control method therefor

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20150062224A1 (en) * 2013-08-27 2015-03-05 Fujifilm Corporation Ink jet recording apparatus and method
US9044984B2 (en) * 2013-08-27 2015-06-02 Fujifilm Corporation Ink jet recording apparatus and method
US10632759B2 (en) * 2017-12-18 2020-04-28 Seiko Epson Corporation Printing control apparatus, printing control system, and printing control method
CN110877484A (zh) * 2018-09-06 2020-03-13 系统科技公司 喷墨印刷方法及喷墨印刷设备
US10603899B1 (en) * 2018-09-06 2020-03-31 Sti Co., Ltd. Inkjet printing method and apparatus

Also Published As

Publication number Publication date
JP2010284878A (ja) 2010-12-24
JP5322786B2 (ja) 2013-10-23
US20100315457A1 (en) 2010-12-16

Similar Documents

Publication Publication Date Title
US20110084996A1 (en) Inkjet recording apparatus and method, and abnormal nozzle detection method
JP4660860B2 (ja) 画像記録方法及び装置
EP1798037B1 (en) Image recording apparatus and image recording method
US8403445B2 (en) Method and apparatus for determining the density unevenness in an ink jet head
EP2422984B1 (en) Defective recording element correction parameter selection chart, defective recording element correction parameter determination method and apparatus, and image forming apparatus
EP1308279B1 (en) Image correction method in inkjet recording apparatus
US9016821B2 (en) Image processing apparatus and image processing method
US8472069B2 (en) Dot position measurement method and apparatus, and computer readable medium
EP3670197B1 (en) Image processing apparatus, image processing method and storage medium
JP5311688B2 (ja) 濃度むら補正値算出方法及び画像処理方法並びに画像処理装置
KR101074591B1 (ko) 액체 토출 장치의 농도 조정 방법, 액체 토출 장치의 농도조정 시스템 및 액체 토출 장치
JP5963457B2 (ja) 画像処理方法および画像処理装置
JP2018058320A (ja) インクジェット装置及びインクジェット装置の濃度調整方法
JP6415080B2 (ja) 画像処理装置、画像処理方法、記録装置及びプログラム
US20050168539A1 (en) Method of selecting inkjet nozzle banks for assembly into an inkjet printhead
JP2006095768A (ja) 画像形成装置及び方法
JP2015003512A (ja) 印刷装置及び吐出異常の検知方法
JP2009241564A (ja) 画像記録装置、画像記録方法、吐出特性検査用チャート、および吐出特性検査方法
US20020171697A1 (en) Method and system for compensating for banding defects in inkjet printers
US20120013674A1 (en) Virtual Pen Calibration
US8388088B2 (en) Dot position measurement method and apparatus, and computer readable medium
JP2015116776A (ja) 記録装置及び記録方法
JP2001322261A (ja) ノズルのずれと副走査送りのずれとに基づいて記録モードを選択して行う印刷
JP6128826B2 (ja) 記録装置、および記録濃度の補正方法
JP4635818B2 (ja) 画像の濃度補正の実行可否の判定方法

Legal Events

Date Code Title Description
AS Assignment

Owner name: OLYMPUS CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:IWASAKI, TADASHI;REEL/FRAME:024508/0116

Effective date: 20100602

AS Assignment

Owner name: ORTEK CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:OLYMPUS CORPORATION;REEL/FRAME:026110/0639

Effective date: 20110318

AS Assignment

Owner name: RISO KAGAKU CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:OLYMPUS CORPORATION;REEL/FRAME:026512/0638

Effective date: 20110614

AS Assignment

Owner name: RISO KAGAKU CORPORATION, JAPAN

Free format text: CHANGE OF NAME;ASSIGNOR:ORTEK CORPORATION;REEL/FRAME:027343/0269

Effective date: 20110930

FEPP Fee payment procedure

Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

STCF Information on status: patent grant

Free format text: PATENTED CASE

FEPP Fee payment procedure

Free format text: PAYER NUMBER DE-ASSIGNED (ORIGINAL EVENT CODE: RMPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

FPAY Fee payment

Year of fee payment: 4

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 8TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1552); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 8

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 12TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1553); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 12